After studying electrical engineering for four years, Kim emigrated to the United States in 1976. While stocking shelves in an automotive parts warehouse, Kim earned an electrical engineering degree at night from California State University at Northridge. After working at several companies, he started making computer network products in his garage in 1984. Seven years later, Kim had sold the firm, Fibermux, for $54 million. In 1993 Kim founded another firm, Xylan, to make routing switches for computer networks. By 1999, the company was worth $1.2 billion and was acquired by Alcatel.